A comparative study of the 370 yr B.P. West Island and 1883 A.D. Burr Point pyroclastic deposits, Augustine Volcano, Alaska

Augustine Volcano (Alaska) is the most active volcano in the eastern Aleutian Islands, with 7 violent eruptions over the past 200 years and at least 12 catastrophic debris-avalanche deposits over the past ∼2,000 years. The frequency and destructive nature of these eruptions represents a significant hazard to the Cook Inlet region of Alaska given its proximity to commercial ports and populated areas. The focus of this study examines the emplacement of pyroclastic density currents by comparing the stratigraphic, granulometric, and petrographic characteristics of pyroclastic deposits emplaced in the 1883 C.E. Burr Point eruption and those emplaced ∼370 14 C yr B.P. during the West Island eruption. Data from this study combines grain size and componentry analysis of pyroclastic deposits with density and textural analysis of juvenile clasts contained in the pyroclastic deposits. Stratigraphic and granulometric data suggest differences in the manner in which these two pyroclastic density currents traveled and groundmass textures are interpreted as recording differences in how the two magmas ascended and erupted. Juvenile Burr Point clasts resemble block and ash flow deposits, vesicular and glassy juvenile West Island clasts bear some resemblance to clasts derived from so-called "blast-generated" pyroclastic density current deposits at Mt. St. Helens in 1980 and Bezymianny in 1956.